The present invention relates to a control valve for a variable displacement compressor that is used in a refrigerant circuit of a vehicle air conditioner and changes the displacement in accordance with the pressure in a crank chamber.
The control valve includes, for example, a valve body, a bellows, and a transmission rod. The opening degree of the valve body is controlled in accordance with the pressure in a crank chamber. The movable end of the bellows is displaced in accordance with the pressure in a suction pressure zone of the refrigerant circuit. The transmission rod couples the valve body to the movable end of the bellows so that the valve body integrally moves with the movable end of the bellows. When the movable end of the bellows is displaced in accordance with the pressure in the suction pressure zone, the valve body moves by means of the transmission rod. The discharge displacement of the compressor is adjusted to cancel the variations of the pressure in the suction pressure zone in accordance with the position of the valve body.
If the movable end of the bellows simply contacts the transmission rod, a measurement error in the bellows during manufacturing may incline the axis of the bellows with respect to the axis of the valve housing. If the inclination of the bellows is great, the bellows contacts the inner wall of a sensing chamber, in which the bellows is accommodated. As a result, the fluctuations of pressure in the suction pressure zone are not reliably communicated to the valve body. That is, the control valve malfunctions.
To reduce the malfunction of the control valve, the following art has been proposed. That is, a recess is formed on the movable end of the bellows. The end of the transmission rod is fitted to the recess. The bellows is supported by a valve housing through the transmission rod. Therefore, the inclination of the bellows caused by a measurement error is corrected. However, due to the correction of the inclination, the elastic bellows generates stress in a direction that intersects the axis of the valve housing. The stress is applied to the transmission rod through the fitted portion. Therefore, the friction between the transmission rod and the valve housing increases due to the stress. As a result, the hysteresis in the operational characteristics of the control valve increases.
The objective of the present invention is to provide a control valve for a variable displacement compressor that suppresses the inclination of a bellows and prevents the transmission rod from being affected by forces applied by the bellows in a direction that intersects the axial direction.
To achieve the foregoing objective, the present invention provides a control valve used for a variable displacement compressor installed in a refrigerant circuit. The compressor varies the displacement in accordance with the pressure in a crank chamber. The compressor has a control passage, which connects the crank chamber to a pressure zone in which the pressure is different from the pressure of the crank chamber. The control valve includes a valve housing, a valve chamber, a valve body, a pressure sensing chamber, a bellows, a transmission rod, and an elastic member. The valve chamber is defined in the valve housing. The valve body is accommodated in the valve chamber for adjusting the opening degree of the control passage. The pressure sensing chamber is defined in the valve housing. The pressure at a pressure monitoring point in the refrigerant circuit is applied to the pressure sensing chamber. The bellows is located in the pressure sensing chamber. The bellows has a movable end. The transmission rod is slidably supported by the valve housing between the valve chamber and the pressure sensing chamber. The transmission rod moves the valve body in accordance with the displacement of the bellows. The bellows is displaced in accordance with the variations of the pressure in the pressure sensing chamber thereby moving the valve body such that the displacement of the compressor is adjusted to cancel the variations of the pressure in the pressure sensing chamber. The movable end of the bellows and the transmission rod contact each other and can be relatively displaced in a direction intersecting the axis of the valve housing. The elastic member is located between the inner wall of the pressure sensing chamber and the movable end of the bellows. The elastic member elastically supports the movable end such that the movable end can be displaced. One of the elastic member and the movable end of the bellows includes a recess and the other one includes a protrusion such that the elastic member and the movable end of the bellows are fitted to each other.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.